1. Technical Field of the Invention
This invention relates to the processing of cigarette tobacco and in particular to the making of cigarettes with reduced packing density without significant loss of firmness using elevated temperatures.
2. Discussion of the Related Art
In the manufacture of cigarettes, as a rule, pneumatic conveying systems are used to transport the cut tobacco filler to the cigarette maker. An air lock at the entrance to the cigarette maker is used to separate the tobacco from the driving air stream, with the tobacco dropping out of the air lock into a hopper. The hopper is equipped with a mechanism to form a uniform tobacco flow, open out the bulk tobacco and generate single fibers, strands, or particles and to eliminate foreign parts and stems. Generally the tobacco is fed in small portions into a reservoir from which a steep angle conveyer belt armed with needles or spikes continuously feeds the tobacco into a bulking chute. A level sensor in combination with a speed control of the steep-angle conveyer belt keeps the level in the hopper constant. At the downstream end of the chute is a discharge roller armed with needles. This roller, or carded drum, picks up the tobacco at a uniform rate, generating a continuous flow of tobacco. A relatively fast rotating picker-roller then combs the tobacco out of the carded drum and projects it into a fast moving air stream belt. This leads substantially to a desirable distribution of single tobacco particles, necessary for the subsequent separation of winnowers, which are generally veins and stems of the tobacco leaf, and for the formation of a relatively uniform tobacco rod. In some machines a rotating collector tube supports the upward acceleration of the fibers. During this transport and heavy particle separation process some degradation of tobacco particles occurs, leading to a loss in quality of resulting cigarettes. The tobacco rod is formed by a narrow perforated conveyor belt of about eight to ten millimeters in width moving quickly at right angles to the direction of pneumatic conveyance. Degradation in cigarette making machines occurs mostly in the elevator conveyor, carding drums and picker winnower assemblies.
Characteristics of cigarettes which are affected by the tobacco are generally considered to include (a) smoking flavor, (b) occurrences of spotting, (c) firmness of the tobacco rod, (d) collapse during smoking, (e) cut strength, and (f) degree of end fallout. Characteristics, or attributes, (c) to (f) are purely physical and normally can be predicted with a high degree of confidence by four properties of the tobacco rod. Those properties are (i) tobacco packing density, (ii) blend filling power, (iii) level and type of add-backs, and (iv) particle size distribution.
The fragility of cigarettes is closely related to the packing density of the tobacco and to particle size. Reduction of the packing density using current manufacturing methods has not been satisfactorily achieved as the resulting cigarettes tend to be too fragile leading to significant handling losses. Further, the tobacco particle size normally found in cigarettes produced by current manufacturing methods is generally well below that which would produce optimum quality cigarettes. There are several reasons for this, including (A) the size of the threshed lamina, (B) the primary processing, (C) the handling of the cut filler, and (D) degradation of tobacco particles in the cigarette making machine.